The present invention relates to molding thermoplastic devices, and in particular, to an adjustable mold which can be used to make variously sized and shaped thermoplastic objects.
In the course of shipping and handling small parts and other objects, it is often desirable that multiple parts be placed into a tray for convenient handling. These trays generally are referred to as "dunnage trays." They typically provide a molded depression which conforms to the shape of the part being handled or shipped. Using a dunnage tray, each part can be placed into its own shape-conforming depression in order to securely hold the part and to protect the part from jostling and damage during the shipment process. Typically dunnage trays are filled by the manufacturer of a small part, and then shipped to a second location where the part is withdrawn from the dunnage tray and used in a manufacturing application. Therefore, the dunnage tray serves not only as a reasonable protective packaging for the small part, but also serves as a transportation vehicle and storage compartment for the small part. Since dunnage trays are most efficiently maintained as a reusable item, it is necessary that they be constructed of a resilient material, and it is helpful if the material is also relatively lightweight so as not to add to shipping costs. In view of these requirements, thermoplastic material has developed as an ideal construction material for dunnage trays and a substantial amount of time and effort and expense is devoted to the designing of efficient dunnage trays which permit safe and secure housing for the parts to be shipped and which conform very closely to the shape of the particular part. Therefore, it will be appreciated that a dunnage tray of a standard shape is of little use to a wide variety of manufacturers. Rather, it is necessary that dunnage trays be specifically designed and produced to hold a particularly shaped part of a single manufacturer. Such individual design and construction of molds to produce dunnage trays is an expensive aspect of dunnage tray production. In the case where a manufacturer is producing a large volume of parts over a significant amount of time, the cost of the dunnage trays becomes an acceptable level of expense which can be amortized over a number of years. However, in the case of a small manufacturer or a limited production of a particular part, it is very difficult to justify the high expense of producing an individual mold for a production of a particular part which may not justify the expense of the dunnage tray over the long term.
Therefore, a need has long existed for a means for reducing the cost of production of dunnage trays by reducing the cost of producing a dunnage tray mold which is particularly suited to an individual part. In order to produce a dunnage tray mold which can be reconfigured easily and conveniently to different parts and different manufacturers, it is necessary that the dunnage tray mold be adaptable to change not only the length, width, and depth of the dunnage tray, but also, the shaping of the interior surface of the dunnage tray so that the interior surface of the tray can conform to whatever part is being shipped in the tray.
An additional problem presented by this art is the need for a vacuum to be applied by the mold form to draw the sheet of thermoplastic material into close contact with the mold to take on the shape presented by the mold. This requires that apertures be incorporated in the mold which allow an applied vacuum to be pulled against the plastic sheet. In the case of an adjustable mold, a substantial difficulty is presented as to how to provide sufficient vacuum ports for large size molds while eliminating those vacuum ports when they are not required for molding smaller pieces. In addition, a further difficulty is presented in that the vacuum must be communicated through the mold form in order to draw down the plastic sheet.
In view of the foregoing difficulties it will be appreciated that a substantial problem is presented in the industry of reducing the cost of production of dunnage trays by reducing molding costs while satisfying the very specific and particularized shape requirements of both the manufacturer and the manufacturer's particular part.